10 Incredible Sea Urchin Facts


sea ​​urchins are small, round, spiny echinoderms of the class Echinoidea. There are approximately 950 species of sea urchins that inhabit the oceans and all depth areas in all climates. They play an important role in the ocean ecosystem, although they face new threats daily.

They come in many colors, from red to purple to green, making them one of the most visible and mesmerizing. Marine animals. A medium sea urchin is small, measuring about 1 to 4 inches in diameter. The giant sea urchin measures approximately 14 inches in diameter. Sea urchins weigh about one pound on average. They move either by propelling themselves with their spines or by crawling slowly with tube feet.

Did you know that the enzymes in the venom of the flower sea urchin are powerful enough to cause severe pain and muscle contractions that can lead to death? You better run if you see a flower urchin underwater!

Here are ten amazing facts you need to know about sea urchins.

1. Sea urchins have no bones in their bodies.

imperial sea urchin
Sea urchins have a shell-like structure known as the test.

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Sea urchins do not have a bony structure. Instead, they have a shell-like structure known as a test, which is made from calcium carbonate. The test consists of small segments of plaque that completely cover the sea urchin. The hard shell somewhat resembles the body of sand dollars and starfish and is their main form of protection.

2. The red sea urchin is the largest of the species

red sea urchin
The red sea urchin is the largest species.


The maximum test diameter of a red sea urchin is about 7 inches, with a spine length of about 2-3 inches. They inhabit the North Pacific waters of America, from as far away as Alaska in Baja California. Red sea urchins are commonly seen in shallow water and on rocky shores that are sheltered from extreme wave action.

3. Sea urchins have a distinctive appearance

sea ​​urchin
Sea urchins develop fivefold symmetry when they become adults.

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Sea urchins have spherical, flattened, or oval bodies covered in rigid exoskeletons and surrounded by spines. The length of these spines varies from species to species. Sea urchin spines are divided into two categories; primary for longer spines and secondary for shorter ones.

Sea urchins have bilateral symmetry as larvae, which means you can split their bodies into two identical halves on both sides. They develop fivefold symmetry when they become adults, which means you can divide their bodies into five similar sections. Their mouth is at the bottom of their body and their anus at the top.

4. Sea urchins can live up to 200 years in the wild

Research suggests sea urchins could live up to 200 years in the wild. Their lifespan is reduced to around 30 years in captivity, while it is generally over 30 years in the wild. The oldest sea urchin ever found was the red sea urchin, which was estimated to be around 200 years old.

It’s possible that these species lived longer in the past, but ever-changing ocean conditions have made it harder for them to survive longer. Oversaturated ocean pollution and increasing fishing by humans constantly put the lives of sea urchins in critical danger. Some of the sea urchins have already been listed as endangered.

5. Sea urchins have a simple nervous system and reproductive period

Technically, sea urchins don’t have brains. Instead, they have very simple nerves that radiate throughout their bodies from a neural ring around their mouths. These nerves allow sea urchins to control their limbs and other body parts. They also give them the sense of touch.

Sea urchins use external fertilization to reproduce. Both females and males release their eggs and sperm into the surrounding water. Therefore, fertilization occurs independently of the parents.

Embryos usually develop within the first twelve hours. They begin to float on the water as they become larvae, allowing currents to carry them along while feeding on phytoplankton. It takes several months for the larvae to become juveniles. The young sea urchin then sinks to the bottom of the sea as the shell continually grows and hardens. Juveniles become adults in about five years but reach sexual maturity in two years.

6. Sea urchins have hundreds of tiny feet.

Sea urchins have pairs of very flexible little limbs called tube feet, which allow them to move quickly in and out of their shell. They use their body’s internal water pressure to move their tube feet. Each tube foot is a small, sucker-like shape that allows the sea urchin to grip surfaces and pull itself forward. This often creates the illusion that they are using their spine to facilitate movement.

7. Sea urchins can hurt people

Sea urchin stings are very dangerous. Their spins are sharp enough to pierce human skin, causing injury. Also, their spines tend to break, which means they penetrate inside the person, leading to more pain and infection. Worse still, their spines are so fragile that they can be difficult to extract.

Sea urchin venom is generally not lethal, although some people are highly allergic to the poison. Hence, it causes a severe reaction in the form of breathing difficulties. This could prove fatal if not followed medically.

8. The flower sea urchin is the most dangerous species

Flower sea urchin close-up.
Flower urchins are commonly found in the Indo-West Pacific region.


Another incredible fact about sea urchins is their potential danger. The flower urchin, in particular, is the deadliest of them all. They are commonly found in the Indo-West Pacific region. Unlike other sea urchins, flower urchins contain deadly venom, which can kill a human. They have two types of venom. The first attacks the nerves and the blood, although it is not dangerous in itself.

The second venom is also not dangerous but makes the first more poisonous. The combination of the two venoms can lead to anaphylactic shock, convulsions and death. Although bites are often fatal, you can survive a bite with proper treatment. The flower sea urchin was named the most dangerous sea urchin in the world by the Guinness Book of World Records in 2014.

9. Sea urchins are omnivores

Purple and red sea urchins eat a piece of kelp.
Sea urchins are primarily omnivorous since they feed on plants and animals.

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A sea urchin’s diet consists mainly of algae, crinoids, brittlestars, sponges, molds and polychaetes. They are mainly omnivores since they feed on plants and animals. Sea urchins play an important role in the ecosystem. They maintain the balance between coral and algae.

In turn, sea urchins are preyed upon by otters, lobsterscrabs and many fish. Otters use their sharp claws and greater strength to wipe away the sea urchin’s spines before snapping it. Using their claws, Crabs and the lobsters break the sea urchin’s spines before getting inside. Predatory fish also bite the spine before opening the shell.

10. Sea urchins are a very delicious food for humans

People all over the world eat sea urchins. They are a key ingredient in mayonnaise and Hollandaise sauce used in fish dishes. In Mediterranean and New Zealand cuisine, chefs serve sea urchins raw or cooked with seasoned lemons. Chileans also eat raw sea urchins. Sea urchins give flavor to soups, soufflés, soups and omelettes, among other European dishes.


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